Absorption in the infrared of surface electromagnetic waves by adsorbed molecules on a copper surface

Abstract

Experimental observations have been made for the first time that surface electromagnetic wave (SEW) spectroscopy can be used to measure the infrared spectra of adsorbed molecules and very thin films on metal surfaces. Using a tunable CO2 laser (9.2–10.8 μm wavelength), the 975 and the 1037 cm−1 resonances of 5–25 Å thick physisorbed benzene on copper were observed. Broadening of these resonances for the thinnest layers of benzene was observed. Also SEW spectroscopy and ellipsometry were used to study thin films of cellulose acetate (15–75 Å) on copper. Further, it was shown that film thicknesses determined by SEW spectroscopy are in agreement with the ellipsometric thicknesses and that the SEW method is more sensitive for very thin (<25 Å) films.